2 Covalent BondsCovalent Molecule – A substance comprised of only nonmetals and metalloidsCovalent BondFormed by the sharing of electronseach atom within the bond achieves an octet (8) except hydrogen (2) and boron (6)Minimize the repulsions and maximize the attractions
4 Naming Binary Molecular Compounds The atoms of a molecular formula are written in the order of the elements electronegativityLeast electronegative atom will always be listed first.Electronegativity – indicates how well an elements nuclei attract the electrons in a covalent bond
6 Naming Covalent molecules Translate the elemental symbol into the elements name1st element – give its name2nd element – gets ending –ide same as found in ionic compoundsBecause electrons are sharedIndicate how many of each atom are present using the prefix systemAll elements will receive a prefix except if there is only 1 of the first element
7 Naming Binary Molecular Componds The prefix mono- is omitted for the first element.
8 Problem What is the name of PCl3? a. phosphorus chloride b. phosphoric chloridec. phosphorus trichlorated. trichlorophosphidee. phosphorus trichloride
9 ProblemThe compound, P4S10, is used in the manufacture of safety matches. What is its name? a. phosphorus sulfideb. phosphoric sulfidec. phosphorus decasulfided. tetraphosphorus decasulfidee. phosphorus sulfide
11 Covalent Bonds and the Periodic Table Covalent bonds form between nonmetalsAchieve an octet (noble gas configuration)Using electron dot symbols buildH2, H2O, CH4, O2, N2, HCN, CO2Least electronegative atom is central (except H)
12 Covalent Bonds and the Periodic Table Elements follow octet ruleH gets 2 electrons – 1 bondB has 3 valence electrons – can only form 3 bondsPeriod 3 elements and higher can form more than an octet because of the empty d-orbitals
13 Covalent Bonds and the Periodic Table Number of bonds formed to achieve octet. Numbers in parentheses indicate possible numbers of bonds that result in exceptions to the octet rule.
14 Multiple Covalent Bonds Single bond: A covalent bond formed by sharing one electron pair.Double bond: A covalent bond formed by sharing two electron pairs.Triple bond: A covalent bond formed by sharing three electron pairs.
15 Molecular Formulas and Lewis Structures Molecular formula: A formula that shows the numbers and kinds of atoms in one molecule of a compound.Structural formula: A molecular representation that shows the connections among atoms by using lines to represent covalent bonds.Lewis structure: A molecular representation that shows both the connections among atoms and the locations of lone-pair valence electrons.
16 Molecular Formulas and Lewis Structures The oxygen atom in H2Oshares 2 bonding pairs of electrons with two hydrogen atomsHas 2 other pairs of valence electrons that are not shared in bonds – lone pairs
17 Drawing Lewis Structures Sum up the valence electrons for all atoms in the moleculeIdentify the atom in the lowest group # (except H) – Least electronegative atomIf both atoms in same group # identify the one in the highest numbered period.Write this symbol as the central atom surrounded by all other atoms
18 Drawing Lewis Structures Place a single bond (-, representing two electrons) between all external atoms and the central atomAdd up the electrons in the bonds and subtract this from the total valence electrons
19 Drawing Lewis Structures Place all other electrons around the outer atoms (in pairs) first giving them an octet (except H)Most electronegative atom firstPlace all remaining electrons around the central atom as lone pairsCheck to see if all atoms have an octetYes – you are doneNo – make multiple bonds
20 Drawing Lewis Structures H, C, N, O, and halogen atoms usually maintain consistent bonding patterns:H forms one covalent bond.C forms four covalent bonds.N forms three covalent bonds and has one lone pair of electrons.O forms two covalent bonds and has two lone pairs of electrons.Halogens form one covalent bond and have three lone pairs of electrons.
21 The Shapes of the Molecules Molecular shapes can be predicted by noting how many bonds and electron pairs surround individual atoms and applying what is called the valence-shell electron-pair repulsion (VSEPR) model.VSEPR model - the negatively charged clouds of electrons in bonds and lone pairs repel each other, and keep as far apart as possible.
22 The Shapes of the Molecules There are three step to applying the VSEPR model:Step 1: Draw a Lewis structure of the molecule, and identify the atom whose geometry is of interest.Step 2: Count the number of electron charge clouds surrounding the atom of interest.Step 3: Predict molecular shape by assuming that the charge clouds orient in space so that they are as far away from one another as possible.
24 The Shapes of the Molecules Linear molecules have bond angles of 180°.Planar triangular molecules have bond angles of 120°.Tetrahedral molecules have bond angles of 109.5°.
25 Polar Covalent Bonds and Electronegativity As a rule of thumbelectronegativity differences of less than nonpolar covalent bondsdifferences up to 1.9 indicate polar covalent bondsdifferences of 2 or more indicate ionic bonds.
26 Problem Select the most polar bond amongst the following. a. C-O b. Si-Fc. Cl-Fd. C-Fe. C-I
27 Polar MoleculesIf the bonds in a molecule have a polarity then depending on the shape of the molecule, the molecule itself can be polarGuaranteed nonpolar moleculesLinear, trigonal planar and tetrahedral if all peripheral atoms are identical